95 research outputs found
\emph{Ab initio} study of (100) diamond surface spins
Unpaired electronic spins at diamond surfaces are ubiquitous and can lead to
excess magnetic noise. They have been observed in several studies to date, but
their exact chemical nature is still unknown. We propose a simple model to
explain the existence and chemical stability of surface spins associated with
the dangling bond on the (100) diamond surface using density functional
theory. We find that the (111) facet, which is naturally generated at a step
edge of (100) crystalline diamond surface, can sterically protect a spinful
defect. Our study reveals a mechanism for annihilation of these surface spins
upon annealing, consistent with recent experimental results. We also
demonstrate that the Fermi-contact term in the hyperfine coupling is not
negligible between the surface spins and the surrounding nuclear spins, and
thus \textit{ab initio} simulation can be used to devise a sensing protocol
where the surface spins act as reporter spins to sense nuclear spins on the
surface.Comment: 11 figure
Electrically driven optical interferometry with spins in silicon carbide
Interfacing solid-state defect electron spins to other quantum systems is an
ongoing challenge. The ground-state spin's weak coupling to its environment
bestows excellent coherence properties, but also limits desired drive fields.
The excited-state orbitals of these electrons, however, can exhibit stronger
coupling to phononic and electric fields. Here, we demonstrate electrically
driven coherent quantum interference in the optical transition of single,
basally oriented divacancies in commercially available 4H silicon carbide. By
applying microwave frequency electric fields, we coherently drive the
divacancy's excited-state orbitals and induce Landau-Zener-Stuckelberg
interference fringes in the resonant optical absorption spectrum. Additionally,
we find remarkably coherent optical and spin subsystems enabled by the basal
divacancy's symmetry. These properties establish divacancies as strong
candidates for quantum communication and hybrid system applications, where
simultaneous control over optical and spin degrees of freedom is paramount.Comment: 17 pages, 4 figure
High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide
Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spinâoptical interfaces are a leading hardware in this regard. However, available systems suffer from large electronâphonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its 4A2 symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with âŒ1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins
BLUF Domain Function Does Not Require a Metastable Radical Intermediate State
BLUF
(blue light using flavin) domain proteins are an important
family of blue light-sensing proteins which control a wide variety
of functions in cells. The primary light-activated step in the BLUF
domain is not yet established. A number of experimental and theoretical
studies points to a role for photoinduced electron transfer (PET)
between a highly conserved tyrosine and the flavin chromophore to
form a radical intermediate state. Here we investigate the role of
PET in three different BLUF proteins, using ultrafast broadband transient
infrared spectroscopy. We characterize and identify infrared active
marker modes for excited and ground state species and use them to
record photochemical dynamics in the proteins. We also generate mutants
which unambiguously show PET and, through isotope labeling of the
protein and the chromophore, are able to assign modes characteristic
of both flavin and protein radical states. We find that these radical
intermediates are not observed in two of the three BLUF domains studied,
casting doubt on the importance of the formation of a population of
radical intermediates in the BLUF photocycle. Further, unnatural amino
acid mutagenesis is used to replace the conserved tyrosine with fluorotyrosines,
thus modifying the driving force for the proposed electron transfer
reaction; the rate changes observed are also not consistent with a
PET mechanism. Thus, while intermediates of PET reactions can be observed
in BLUF proteins they are not correlated with photoactivity, suggesting
that radical intermediates are not central to their operation. Alternative
nonradical pathways including a ketoâenol tautomerization induced
by electronic excitation of the flavin ring are considered
Sources of Variation in Physician Adherence with Clinical Guidelines: Results from a Factorial Experiment
BACKGROUND: Health services research has documented the magnitude of health care variations. Few studies focus on provider level sources of variation in clinical decision making-for example, which primary care providers are likely to follow clinical guidelines, with which types of patient. OBJECTIVES: To estimate: (1) the extent of primary care provider adherence to practice guidelines and the unconfounded influence of (2) patient attributes and (3) physician characteristics on adherence with clinical practice guidelines. DESIGN: In a factorial experiment, primary care providers were shown clinically authentic video vignettes with actors portrayed different âpatientsâ with identical signs of coronary heart disease (CHD). Different types of providers were asked how they would manage the different âpatientsâ with identical CHD symptoms. Measures were taken to protect external validity. RESULTS: Adherence to some guidelines is high (over 50% of physicians would follow a third of the recommended actions), yet there is low adherence to many of them (less than 20% would follow another third). Female patients are less likely than males to receive 4 of 5 types of physical examination (pâ<â.03); older patients are less likely to be advised to stop smoking (pâ<â.03). Race and SES of patients had no effect on provider adherence to guidelines. A physiciansâ level of experience (age) appears to be important with certain patients. CONCLUSIONS: Physician adherence with guidelines varies with different types of âpatientâ and with the length of clinical experience. With this evidence it is possible to appropriately target interventions to reduce health care variations by improving physician adherence with clinical guidelines
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